1. Technical Field
The present invention generally relates to a semiconductor memory device. More specifically, the present invention relates to a semiconductor memory device having a three-dimensionally stacked memory cells.
2. Related Art
Nonvolatile memory devices are data storage units capable of holding their data even when power supplied thereto is suspended or shut off. Coming up to the limit to integration capacity of second-dimensional memory devices where memory cells are formed by a unitary layer on a silicon substrate, three-dimensional (3D) nonvolatile memory devices by the architecture of vertically stacking memory cells from silicon substrates are being steadily proposed.
The 3D nonvolatile memory devices usually include interlayer insulating layers and word lines, which are alternately stacked, and channel layers vertically penetrating the interlayer insulating layers and the word lines. Along the channel layers, memory cells are stacked. In manufacturing 3D nonvolatile memory devices, the stacked word lines are formed by substituting a plurality of conductive layers for a plurality of nitride layers after alternately stacking a plurality of oxide layers and the nitride layers.
However, it is quite difficult to perform the process of substituting conductive layers for nitride layers. Especially, while substituting the conductive layers for the nitride layers, there is a problem of causing the stacked structure to lean.